GranQuartz is now offering a line of Stone Pro ADA-compliant Vanity Supoorts that allow for easy install of ADA-compliant, wheelchair accessible vanity tops. The ADA Vanity Supports have a 4-ft. span with two brackets, a 5-ft. span with three brackets or an 8-ft. or larger span with four or more brackets depending on the compliant spacing needed.
You may also be interested in this article on ADA compliant sinks.